Experimental Generation Atom-Photon Entanglement Sources By Spontaneous Raman Scattering Process

Atom-photon entanglement sources,an important resource in the DLCZ(Duan-Lukin-Cirac-Zoller)scheme of quantum repeater,play a crucial role in entanglement swapping,quantum state storage and entanglement purification.In 2001,Duan and others proposed the DLCZ quantum repeater scheme,in which a non-classical correlation between scattered photons and spin waves in spontaneous Raman scattering process was proposed to construct quantum repeater.The experimental study on atom-photon entanglement sources had drawn great public attention.Subsequently,Duan and others achieved many important results[1,2].In the DLCZ protocol,the cold atom ensemble generates directly atom-photon entanglement sources in the process of spontaneous Raman scattering process.This process is used to realize the entangled storage.This is called the “writing” process;then to realize the entanglement between two photons by reading the spin wave in the atomic ensemble and converting it into a single photon.This process is called the “reading” process[3,4].During the writing process,the entanglement between the atomic ensemble and the photon is established and the generated entangled single photon is used to join two separate nodes in entanglement and exchange,while the spin wave stored in the atomic ensemble is ready for future reading and use.Therefore,the entanglement sources are the core component of quantum repeater and its quality is essential[5,6].Utilizing the spontaneous Raman scattering process to generate atom-photon entanglement sources in the cold atom ensemble,this paper studies the relationship between the anti-Stokes photon retrieval efficiency and the optical thickness OD and read power of the cold atom ensemble.Then this paper studies the relationship between the atom-photon entanglement mass and the anti-stokes photon retrieval efficiency,and measured the storage lifetime of the entangled source in the atomic ensemble.Through the research of this thesis,we choose the appropriate parameters to optimize the quality of atom-photon entanglement,which lays a foundation for the experimental study of the long-life and high retrieval efficiency of atom-photon entanglement,The main contents of this paper are:(1)Reviewing the basic principle of scheme of quantum repeater and DLCZ quantum repeater scheme,this paper introduces the capture scheme of cold atom ensemble and the generation scheme of atom-photon entanglement and the experimental progress of the generation of atom-photon entanglement in recent years.(2)This paper introduces the basic principle of generating atom-photon entanglement in the process of spontaneous Raman scattering process.Besides,this paper makes a detailed summary on the entanglement characteristics of atom-photon from the anti-Stokes photon retrieval efficiency,second-order correlation function and Bell parameter S.(3)Experimental studies on the generation of atom-photons entanglement are carried out by using the spontaneous Raman scattering process in the cold atom ensemble.By changing the optical power of the re-pumped light to affect the optical thickness of the captured atoms,the effect of the optical thickness of the cold atomic ensemble and the read optical power on the retrieval efficiency is expanded.As the optical thickness OD gradually increases,the retrieval efficiency of the atom-photon increases from 2.1% to 18%.In the study of the effect of read optical power on retrieval efficiency,we measured the atom-photon retrieval efficiency,noise,and all the signal counts collected by the detector as a function of the read optical power.By measuring,we find that the influence of noise on signal acquisition basically maintains a stable value,and the retrieval efficiency of the atom-photon entanglement and the total detection count show the same trend with the change of read optical power,and this growth trend slows as the reading power increases to 1.5m W.In addition,we also studied the effect of retrieval efficiency on the entanglement of atom-photon,The variation of Bell parameter S value with retrieval efficiency was measured by comparing two different write light excitation rates.The results show that the retrieval efficiency at the two different excitation rates is basically the same as the change in the Bell parameter S value.However,when the excitation rate is 1%,the S value measured by the same reading power is slightly higher than the measured S value when the excitation rate is 1.5%.At the same time,the measured S value of the system is up to 2.6,and the system is entangled when the retrieval efficiency is higher than 0.6%.(4)This paper makes a summary on the research content.The experimental studies on the atom-photon entanglement in this paper can optimize the entanglement characteristics of the entanglement source.Then this paper will carry out the experiment study on the preparation of long-life atom-photon entanglement sources.